Membranous nephropathy is an immune disease in which immune complexes are deposited under the glomerular epithelium, damaging the filtration barrier and resulting in severe proteinuria.　Recently, a new technology called laser microdissection-liquid chromatography mass spectrometry （LMD-LCMS/MS） has been applied to pathological tissue sections, revealing the causative antigens of this disease.　As a result, many causative antigens, including phospholipase A2 receptor （PLA2R）, which is found in 70% of membranous nephropathy cases, have been identified as proteins expressed in glomerular podocytes.　Corresponding autoantibodies are detected in the blood, leading to the understanding that membranous nephropathy is an autoimmune disease targeting podocytes.　In addition, since the autoantibody subclass is IgG4, this disease can be considered an IgG4-related autoimmune disease.　Membranous nephropathy was previously classified as idiopathic or secondary, but with the identification of causative antigens, it is now classified based on the specific antigen involved.　The elucidation of the pathogenesis and selection of treatment strategies have begun based on the causative antigen and the characteristic IgG4 immune response in membranous nephropathy.